1. Field of the Invention
The present invention is related to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and a method of handling a device-to-device communication in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple user equipments (UEs), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Device-to-device (D2D) communication may be realized, after an initialization (e.g., connection establishment and/or peer discovery) is performed (e.g., assisted by an eNB). Then, two UEs may communicate (e.g., transmitting and/or receiving packets) with each other (e.g., directly) according to the D2D communication, and the eNB may not need to forward the packets transmitted between the UEs. According to the D2D communication, the UEs may communicate with each other via UL resources (e.g., UL subframes configured by the eNB). In general, the D2D communication may also be seen as a D2D service (i.e., proximity-based service (ProSe)). The D2D service can be a ProSe direct discovery or a ProSe direct communication. In addition, a D2D subframe, D2D transmission, D2D communication and D2D discovery can be termed as a sidelink subframe, sidelink transmission, sidelink communication and sidelink discovery, respectively.
In certain situations, an eNB (or radio access network (RAN)) may control multiple public land mobile networks (PLMNs) (i.e., the eNB (or RAN) is shared by the PLMNs), and the eNB broadcasts PLMN identities of the PLMNs to UEs. A monitoring UE in a coverage area of the eNB (e.g., camping on the eNB) may receive both an announcement message (e.g., for ProSe discovery) transmitted by an announcing UE and the PLMN identities. The monitoring UE is not able to determine a monitored PLMN according to the announcement message and the PLMN identities. The monitored PLMN may be a PLMN in which the monitoring UE has monitored a ProSe Application Code. A ProSe function of a PLMN that assigns the ProSe Application Code may perform improper operations, if the monitoring UE reports a wrong monitored PLMN identity to the Prose function. The Prose function may be a ProSe Function of a home PLMN (HPLMN) of the announcing UE. The improper operations may include that the ProSe function incorrectly determines that a received ProSe Application Code is authorized (or not authorized) to be transmitted on the monitored PLMN.
Thus, it is important to solve the reception/transmission of multiple PLMN identities when the eNB are shared by the PLMNs.